Careful patient selection, combined with the management of patient expectations is essential to maximizing visual outcomes and patient satisfaction. Patients should receive information regarding the risks and benefits of SMILE, and informed consent is necessary. Providing patients information on what they might expect to hear, feel, see, and smell during the procedure may serve to reduce patients’ anxiety. Patients’ medical history should be screened for any contraindications, as listed above. Most importantly, patients should only be selected if they have realistic expectations of postoperative visual outcomes. It should be made clear to patients that the goal of laser refractive surgery is not to obtain the complete absence of refractive error but rather lessen one’s reliance on glasses and contacts.

An extensive preoperative evaluation is necessary to identify potential contraindications to laser refractive surgery. Eyelids and tear film require an examination for signs of dry eye or blepharitis. The patient’s refraction, including refractive stability, degree of refractive error, and astigmatism, should be obtained. Both manifest and cycloplegic refraction are necessary; disparities between these two values greater than 1 D of sphere warrants reevaluation. The clinician should inspect the cornea for scars, vessels, or signs of inflammation. Pupil size requires measurement with the commercial pupillometer. The slit-lamp examination allows for the identification of corneal abnormalities such as keratoconus, neovascularization, scarring, or the presence of a cataract. Corneal pachymetry is an excellent screening tool for patients with corneal thinning disorders. Computed corneal topography additionally allows for the detection of keratoconus and irregular astigmatism. Intraocular pressure should be obtained to identify uncontrolled glaucoma. Fundoscopy rules out the presence of retinal holes, degenerative retina, and other types of macular disease. Computed videokeratography identifies early keratoconus, corneal warpage, and asymmetrical or irregular astigmatism.[9]

Immediately before SMILE, topical antibiotics, and topical proparacaine, 0.5% gets instilled in both eyes. Excessive instillation of topical anesthetic should be avoided as this may loosen the corneal epithelium and increase the risk for the formation of black spots and epithelial defects.[8]

Patient positioning should be such that they are comfortable throughout the procedure. The patient’s neck should not be in a twisted posture, and their legs should remain uncrossed. The patient should be advised to take shallow breaths to reduce movement of the head. Proper orientation of the head is crucial to guaranteeing correct docking and centration. The patient should be advised to stay calm, maintain fixation, and avoid squeezing the eye. Patient cooperation through the procedure is of the utmost importance.

Initial docking requires the use of a disposable curved contact glass. The surgeon should verify that proper docking has occurred before initiating corneal contact with the contact glass interface. The patient is then instructed to fixate on a green blinking light to achieve centration. After that, suction is initiated and maintained throughout the procedure. The femtosecond laser generates four sequential photoablative incisions that form an intrastromal lenticule, as well as a small 2.5 mm incision along the superior or superotemporal aspect of the cornea for lenticule access and extraction. The total time for the formation of all incisions by the femtosecond laser ranges between 20 and 35 seconds regardless of the magnitude of refractive error. The surgeon may then use a manual spatula to separate the residual lenticular appendages along the anterior and posterior plane and forceps to extract the lenticule.

Lenticule extraction is often the most challenging step for inexperienced surgeons. Incorrect identification of the tissue plane may result in adherence of the posterior lenticule surface to the stromal surface of the cap.[2] The meniscus sign, which refers to the meniscus-shaped gap between the inner ring and lenticule edge, is one method of clearly discerning the posterior plane during the formation of the posterior lamellar channel.[8] Should improper lenticule dissection occur, the surgeon may struggle to distinguish between the lenticule edge, and the anterior dissection plane as countertraction from the corneal stroma has been lost. Various techniques have been described to facilitate the separation of the lenticule edge from the overlying cap. The push-up technique employs a Y-shaped tip to engage the lenticule edge and enhance it by pushing it up from the stromal bed.[8] Alternatively, anterior segment optical coherence tomography (ASOCT) is another option; dissection planes appear hyperreflective on ASOCT.[8] A newer method known as “lenticuloschisis” allows for the lenticule to be directly peeled off from the surrounding stroma and extracted without the use of an actual dissector. This technique has been suggested to result in a smooth interface, earlier visual recovery, and better visual quality in the immediate postoperative period due to minimal manipulation of tissues.[1]

Occasionally, the lenticule may be retained in the stromal bed. This intraoperative complication can be addressed immediately by conversion to a FLEx procedure if the entire lenticule remains intact. Alternatively, customized surface ablation is a surgical option, though this has limitations with postoperative haze, which may cause poor visual outcomes.[8] In the very rare situation in which lenticule extraction is not possible, or a lenticule remnant is retained in the stromal bed postoperatively, irregular astigmatism may occur.[2]; this complication has undergone effective treatment with transepithelial phototherapeutic keratectomy (PTK).[1]

Medications typically administered during the postoperative period include topical steroids (dexamethasone 0.1%) and topical fluoroquinolone eye drops (moxifloxacin 0.5%) several times daily. These medications, as well as lubricating eye drops, may be recommended for one to two weeks postoperatively. Patients should be closely followed by their ophthalmologist in the weeks to months immediately following SMILE.

Most intraoperative complications associated with SMILE are related to the steep learning curve and relative complexity of the procedure.[10]

Intraoperative complications may be broadly categorized as related to

1. Lenticule creation
2. Lenticule dissection
3. Lenticule extraction.

Lenticule Creation: complications from lenticule creation include suction loss, the formation of an opaque bubble layer (OBL), subconjunctival hemorrhage, incisional bleeding, and black spots. Loss of suction occurs in approximately 6% of cases and is typically due to patient eye contraction or sudden patient movement.[2][10] There has been speculation that operating in the fast mode of the femtosecond laser reduces the incidence of suction loss.[10] Management of suction loss depends upon the point in surgery in which this complication occurs. If loss of suction occurs when less than 10% of the lenticule has been cut, re-docking and re-centration are appropriate. If more than 10% of the lenticule has been cut, the procedure should convert to excimer laser ablation (PRK/LASIK); most patients who experience suction loss and are treated appropriately still experience excellent visual outcomes.[8] OBL is secondary to the accumulation and opacification of bubbles in the intrastromal interface. They can be managed intraoperatively by massaging out bubbles from the interface. OBL is associated with delayed visual recovery but otherwise results in good long-term visual outcomes.[8] Black spots occur due to entrapment of debris or air bubbles between the contact lens and the cornea. They may be addressed by cleaning the contact lens and/or ocular surface and do not typically impact visual outcomes.[8]

Lenticule Dissection or lenticule Extraction: common complications that occur secondary to lenticule dissection or extraction include lenticule remnant, corneal abrasion, lenticule adhesions, and incisional tears. Lenticule remnant and lenticule adhesions may be addressed intraoperatively or postoperatively, as described above. Peripheral corneal abrasions occur in 5.5% of cases and are typically due to excessive manipulation.[2][11] As with other intraoperative complications, the incidence of corneal abrasions shows an inverse correlation to the surgeon’s expertise.[12] Incisional tears occur in 9.6% of patients and may be secondary to surgeon inexperience or the patient suddenly moving the eye while the extraction instrument is inside of the SMILE pocket. One method to prevent this complication is manual fixation of the eye intraoperatively.[2] Both corneal abrasions and incisional tears are manageable with artificial tears and a bandage contact lens postoperatively and do not usually affect visual outcomes.[11]

Primary complications experienced after SMILE include[4]:

• Dry eye
• Corneal abrasion
• Infectious keratitis.

Postoperative dry eye occurs in approximately 3% of patients and is likely multifactorial, attributable to decreased trophic influence in the corneal epithelium, inflammation, damage to limbal goblet cells during suction, and impaired corneal sensation to blink.[2][13] Notably, most studies have reported lower symptoms of dry eye in the immediate postoperative period following SMILE than femtosecond LASIK.[13] This finding has had quantitative verification through differences in tear film break up, corneal sensitivity, and corneal nerve regeneration, all of which are higher in SMILE than femtosecond LASIK.[1] The incidence of infectious keratitis is largely reducible through adherence to a postoperative topical antibiotic regimen. Patients presenting with infectious keratitis should receive prompt irrigation with bactericidal povidone-iodine and an antibiotic solution.[11] Other rare postoperative complications include epithelial ingrowth, irregular topography, micro striae, and interface inflammation.[2] All known instances of ectasia that have occurred after SMILE were in eyes with diagnosed or undiagnosed forme fruste keratoconus.[3]

Numerous meta-analyses have demonstrated that long-term efficacy, predictability, and safety outcomes of SMILE are comparable to those of femtosecond-LASIK.[2][14] A recent multicenter study demonstrated that 88% and 98% of eyes were within +/- 0.5 and +/- 1 D of the targeted correction at three months postoperatively.[15] Other studies have demonstrated that 61-96% of patients achieve a long-term uncorrected distance visual acuity (UDVA) of 20/20 or better.[1]

Current research has suggested numerous benefits of SMILE over femtosecond LASIK. Numerous clinical trials have demonstrated reduced postoperative dry eye associated with SMILE than LASIK.[13] There appears to be significantly fewer HOAs following SMILE[2]; this may be due to a more uniform corneal refractive power.[6] Moreover, there fewer inflammatory cells have been found in corneas following SMILE as compared to femtosecond LASIK.[2] Patients who undergo SMILE tend to have a higher satisfaction trend and vision-related quality of life than those who undergo LASIK.[16][17] SMILE has been demonstrated to result in less severe denervation and accelerated neuronal healing as compared to femtosecond LASIK.[2] Recent studies support the notion that SMILE results in superior corneal biomechanical stability than femtosecond LASIK, as measured by the corneal hysteresis and corneal resistance factor.[1][2] However, given that SMILE is a relatively recent development within the field of laser refractive surgery, further clinical trials are warranted to validate the proposed advantages of SMILE over femtosecond LASIK.

There are some drawbacks with the use of SMILE as compared to femtosecond LASIK. Patient-reported discomfort is often higher during tissue manipulation in SMILE than flap lifting in LASIK; for this reason, inexperienced surgeons should consider administering more topical anesthesia or prescribing anxiolytics or sedatives before surgery.[17] Patients who undergo SMILE tend to describe issues with light sensitivity and blurring of vision at one month postoperatively more often than patients who undergo femtosecond LASIK; however, these concerns tend to resolve as early as three months postoperatively.[17] Visual recovery may be slower in SMILE than femtosecond LASIK. At three months postoperatively, there appears to be more backscatter in eyes treated with SMILE, though there is no significant difference at six months postoperatively.[1][2]

Notably, SMILE has shown slightly worse outcomes for the treatment of low-to-moderate astigmatism than LASIK, but comparable results in the correction of high astigmatism.[6][18] Undercorrection occurs in 11% of patients with astigmatism who undergo SMILE; this is likely due to the lack of cyclotorsion control or eye-tracking technology in the Visumax platform.[2][19] To overcome this lack of control, some authors have recommended making limbal marks at 0 and 180 degrees on the cornea preoperatively while the patient is sitting; when the patient is in the supine position during the procedure, the limbal markings can indicate the degree to which cyclotorsion is present.[6]

Though most SMILE patients are satisfied with their long-term visual outcomes, approximately 3% undergo enhancement procedures within two years of their initial procedure.[20] Risk factors for enhancement include older age, greater preoperative myopia, higher preoperative astigmatism, and intraoperative loss of suction.[6] Retreatment is far more likely to occur due to under-correction rather than overcorrection.[20] Because a significant proportion of SMILE patients continue to experience impairment of corrected distance visual acuity (CDVA) up to three months postoperatively, enhancement procedures should be delayed to allow sufficient time for recovery of visual function.[2]

Of note, there remains no consensus on the best procedure for retreatment after SMILE. Among the numerous options proposed include repeat SMILE below the cap, surface ablation (PRK) augmented by mitomycin-C (MMC), thin-flap LASIK in the cap, or cap-to-flap (also known as the CIRCLE approach).[2] Repeat SMILE has negligible data to support its efficacy and safety and has been advised against by some authors due to the risk of creating multiple dissection planes.[8] Surface ablation with MMC carries the advantages of being relatively simple and circumventing flap formation, thereby maintaining the biomechanical strength of the cornea; however, it correlates with increased postoperative pain and slower visual recovery.[21] Thin-flap LASIK is similarly easy to perform, and additionally results in minimal postoperative pain and a speedy recovery; however, it carries the risk of flap-related complications. Furthermore, limited data exist to support its efficacy and safety in retreatment following SMILE. Some authors have recommended that thin-flap LASIK should only be an option in patients with cap thickness over 135 um and low refractive error.[21] Lastly, the CIRCLE approach, in which the SMILE cap converts into a full flap, results in minimal pain, speedy recovery, and has significant data to support its efficacy and safety; however, this method carries the risk of flap-related complications and is relatively difficult to perform.[21]

Some emerging developments include the potential use of SMILE or lenticule implantation procedures for the treatment of hyperopia. Limited research has suggested that SMILE results in similar visual outcomes, recovery rate, and safety outcomes as hyperopic LASIK.[4] Moreover, hyperopic SMILE correlates with less postoperative inflammation. However, until SMILE has received approval by the FDA for treatment of hyperopia, long-term safety and efficacy data as compared to other laser refractive procedures will not be available.[1] Two lenticule implantation techniques, lenticule intrastromal keratoplasty (LIKE) and small incision lenticule intrastromal keratoplasty (sLIKE), have been developed for the treatment of high hyperopia. In both procedures, a minus lenticule is centrally placed on the optical axis within a stromal pocket. A pilot study of 10 eyes who underwent LIKE resulted in 90% within +/- 1 D of target refraction at six months. The small incision variant would be expected to result in less injury to the subbasal nerve plexus, greater corneal strength, and less flap-related complications.[4] Further trials are warranted to evaluate the efficacy and safety of these two procedures.

Another area of ongoing research is the combination of SMILE with accelerated corneal cross-linking (CXL), also known as SMILE XTRA. This procedure requires the intraoperative injection and application of 0.25% riboflavin in the stromal interface for 1 minute, following by 75 second of UV-A radiation exposure. This procedure is hypothesized to improve the accessibility of laser refractive surgery to individuals with thin corneas at baseline by minimizing the risk of postoperative ectasia. Recent trials on SMILE XTRA have shown promise, but the long-term effects still need to be evaluated.[1]

An interprofessional team of ophthalmic surgeons, nurses, optometrists, and technicians may be involved in the preoperative evaluation, surgery, and postoperative management of patients who undergo SMILE. Ensuring appropriate patient selection per established guidelines and maintaining adequate follow-up are essential for maximizing long-term visual outcomes and patient satisfaction. Nursing should assist during the surgery, and provide post-operative care following. They can also ensure patient compliance and be available for questions in the time after the procedure. All interprofessional healthcare team members should be aware of clinical signs and symptoms suggestive of major postoperative complications, and prompt referral to a cornea specialist is warranted should any of these complications arise. [Level 5]

Nurses should ensure that the patient has signed the consent. Even though the procedure is of relatively short duration, the patient requires monitoring by a nurse. During the procedure, the patient must remain still, and the nurse should take measures to avoid unnecessary anxiety. After the procedure, the patient is monitored by the nurse for a few hours before discharge.

Prior to discharge, the nurse should again emphasize the post-operative instructions. The patient should return to see the ophthalmologist as scheduled. The patient should not scratch the eyes and wear an eye covering when sleeping. During the first week, the recommendation is for the patient to wear eyeglasses when going outdoors.